Monolithic clock generator and timing/frequency reference

Abstract

In various embodiments, the invention provides a clock generator and/or a timing and frequency reference, with multiple operating modes, such power conservation, clock, reference, and pulsed modes. The various apparatus embodiments include a resonator adapted to provide a first signal having a resonant frequency; an amplifier; a temperature compensator adapted to modify the resonant frequency in response to temperature; and a process variation compensator adapted to modify the resonant frequency in response to fabrication process variation. In addition, the various embodiments may also include a frequency divider adapted to divide the first signal having the resonant frequency into a plurality of second signals having a corresponding plurality of frequencies substantially equal to or lower than the resonant frequency; and a frequency selector adapted to provide an output signal from the plurality of second signals. The output signal may be provided in any of various forms, such as differential or single-ended, and substantially square-wave or sinusoidal.

1. An apparatus, comprising:
 a reference resonator adapted to provide a first reference signal having a resonant frequency; 
 a frequency controller coupled to the reference resonator, the frequency controller adapted to be calibrated to determine the resonant frequency having a first frequency of a plurality of frequencies; and 
 an amplifier coupled to the reference resonator; 
 wherein the frequency controller further comprises:
 a temperature compensator coupled to the amplifier; 
 a voltage isolator coupled to the reference resonator; and 
 a process variation compensator coupled to the reference resonator. 
 
 
     
     
       2. The apparatus of  claim 1 , further comprising:
 a frequency divider coupled to the reference resonator, the frequency divider adapted to divide the first frequency by a rational number into a plurality of second signals having a corresponding plurality of frequencies, the plurality of frequencies substantially equal to or lower than the first frequency. 
 
     
     
       3. The apparatus of  claim 2 , wherein the frequency divider further comprises a square-wave generator, the square-wave generator adapted to convert the first reference signal into a substantially square-wave signal having a substantially equal high and low duty cycle. 
     
     
       4. The apparatus of  claim 2 , further comprising:
 a frequency selector coupled to the frequency divider, the frequency selector adapted to provide an output signal from the plurality of second signals. 
 
     
     
       5. The apparatus of  claim 4 , further comprising:
 a mode selector coupled to the frequency selector, the mode selector adapted to provide a plurality of operating modes, the plurality of operating modes selected from a group comprising a clock mode, a timing and frequency reference mode, a power conservation mode, and a pulse mode. 
 
     
     
       6. The apparatus of  claim 5 , further comprising:
 a synchronization circuit coupled to the mode selector; and 
 a controlled oscillator coupled to the synchronization circuit and adapted to provide a third signal; 
 wherein in the timing and frequency reference mode, the mode selector is further adapted to couple the output signal to the synchronization circuit to control timing and frequency of the third signal. 
 
     
     
       7. The apparatus of  claim 6 , wherein the synchronization circuit is a delay-locked loop, a phase-locked loop, or an injection locking circuit. 
     
     
       8. An apparatus, comprising:
 a reference resonator adapted to provide a first reference signal having a resonant frequency; 
 a frequency controller coupled to the reference resonator, the frequency controller adapted to be calibrated to determine the resonant frequency having a first frequency of a plurality of frequencies; and 
 an amplifier coupled to the reference resonator, said amplifier comprising a negative transconductance amplifier; 
 wherein the frequency controller is further adapted to modify a current through the negative transconductance amplifier in response to temperature; 
 wherein the frequency controller further comprises a current source responsive to temperature; and 
 wherein the current source further comprises one or more CTAT, PTAT, or PTAT 2  configurations. 
 
     
     
       9. The apparatus of  claim 8 , wherein the frequency controller is further adapted to modify a current through the negative transconductance amplifier to modify the resonant frequency of the reference resonator. 
     
     
       10. An apparatus, comprising:
 a reference resonator adapted to provide a first reference signal having a resonant frequency; 
 a frequency controller coupled to the reference resonator, the frequency controller adapted to be calibrated to determine the resonant frequency having a first frequency of a plurality of frequencies; and 
 an amplifier coupled to the reference resonator, said amplifier comprising a negative transconductance amplifier; 
 wherein the frequency controller is further adapted to modify a current through the negative transconductance amplifier in response to temperature; and 
 wherein the frequency controller is further adapted to modify a transconductance of the negative transconductance amplifier to modify the resonant frequency of the reference resonator. 
 
     
     
       11. The apparatus of  claim 10 , wherein the frequency controller further comprises a voltage isolator coupled to the reference resonator and adapted to substantially isolate the reference resonator from a voltage variation. 
     
     
       12. The apparatus of  claim 11 , wherein the voltage isolator comprises a current mirror having a cascode configuration. 
     
     
       13. The apparatus of  claim 10 , wherein the frequency controller is further adapted to modify a capacitance or modify an inductance of the reference resonator in response to a temperature variation, a voltage variation, or both a temperature and voltage variation. 
     
     
       14. An apparatus, comprising:
 a reference resonator adapted to provide a first reference signal having a resonant frequency; and 
 a frequency controller coupled to the reference resonator, the frequency controller adapted to be calibrated to determine the resonant frequency having a first frequency of a plurality of frequencies, said frequency controller further comprising: 
 a first array having a plurality of switchable capacitive modules coupled to the reference resonator, each switchable capacitive module having a fixed capacitance and a variable capacitance, each switchable capacitive module responsive to a corresponding coefficient of a first plurality of calibration coefficients to switch between the fixed capacitance and the variable capacitance and to switch each variable capacitance to a control voltage. 
 
     
     
       15. The apparatus of  claim 14 , wherein the frequency controller further comprises:
 a second array having a plurality of switchable resistive modules having a capacitive module, the capacitive module and the plurality of switchable resistive modules further coupled to a node to provide the control voltage, each switchable resistive module responsive to a corresponding coefficient of a second plurality of coefficients to switch the switchable resistive module to the control voltage node; and 
 a temperature-dependent current source coupled through a current mirror to the second array. 
 
     
     
       16. An apparatus, comprising:
 a reference resonator adapted to provide a first reference signal having a resonant frequency; and 
 a frequency controller coupled to the reference resonator, the frequency controller adapted to be calibrated to determine the resonant frequency having a first frequency of a plurality of frequencies; 
 wherein the frequency controller further comprises:
 an array having a plurality of switchable variable capacitive modules coupled to the reference resonator, each switchable variable capacitive module responsive to a corresponding coefficient of a first plurality of calibration coefficients to switch between a first voltage and a second voltage. 
 
 
     
     
       17. The apparatus of  claim 16 , wherein at least one of the first voltage and second voltage is a fixed voltage. 
     
     
       18. The apparatus of  claim 16 , wherein at least one of the first voltage and second voltage is a variable voltage. 
     
     
       19. An apparatus, comprising:
 a reference resonator adapted to provide a first reference signal having a resonant frequency; and 
 a frequency controller coupled to the reference resonator, the frequency controller adapted to be calibrated to determine the resonant frequency having a first frequency of a plurality of frequencies;
 wherein the frequency controller further comprises:
 an array having a plurality of switchable capacitive modules coupled to the reference resonator, each switchable capacitive module having a fixed capacitance and a fuse, each switchable capacitive module responsive to a corresponding coefficient of a first plurality of calibration coefficients to open circuit the fuse. 
 
 
 
     
     
       20. An apparatus, comprising:
 a reference resonator adapted to provide a first reference signal having a resonant frequency; 
 a frequency controller coupled to the reference resonator, the frequency controller adapted to be calibrated to determine the resonant frequency having a first frequency of a plurality of frequencies; and 
 a frequency calibration module coupled to the frequency controller, the frequency calibration module adapted to determine the calibration of the frequency controller in response to a second reference signal; 
 wherein the frequency calibration module comprises:
 a frequency divider coupled to the frequency controller, the frequency divider adapted to convert an output signal derived from the first reference signal having the first frequency to a lower frequency to provide a divided signal; 
 a frequency detector coupled to the frequency divider, the frequency detector adapted to compare the second reference signal to the divided signal and provide one or more up signals or down signals; and 
 a pulse counter coupled to the frequency detector, the pulse counter adapted to determine a difference between the one or more up signals or down signals as an indicator of a difference between the output signal and the second reference signal. 
 
 
     
     
       21. The apparatus of  claim 20 , wherein the reference resonator comprises an inductor (L) and a capacitor (C) coupled to form an LC-tank. 
     
     
       22. The apparatus of  claim 20 , wherein the reference resonator comprises at least one of the following resonators: a ceramic resonator, a mechanical resonator, a microelectromechanical resonator, and a film bulk acoustic resonator. 
     
     
       23. The apparatus of  claim 20 , wherein the apparatus is integrated monolithically with a second circuit to form a single integrated circuit. 
     
     
       24. The apparatus of  claim 23 , wherein the second circuit is a microprocessor, a digital signal processor, a radio frequency circuit, or a communications circuit. 
     
     
       25. An apparatus, comprising:
 a reference resonator adapted to provide a first reference signal having a resonant frequency; 
 a frequency controller coupled to the reference resonator, the frequency controller adapted to be calibrated to determine the resonant frequency having a first frequency of a plurality of frequencies; 
 a second oscillator providing a second oscillator output signal; and 
 a mode selector coupled to the frequency controller and to the second oscillator, the mode selector adapted to switch to the second oscillator output signal to provide a power conservation mode. 
 
     
     
       26. The apparatus of  claim 25 , wherein the second oscillator is a ring oscillator, a relaxation oscillator, or a phase shift oscillator. 
     
     
       27. An apparatus, comprising:
 a reference resonator adapted to provide a first reference signal having a resonant frequency; and 
 a frequency controller coupled to the reference resonator, the frequency controller adapted, when calibrated, to select the resonant frequency having a first frequency of a plurality of frequencies; 
 wherein the frequency controller further comprises:
 a first array having a plurality of switchable capacitive modules coupled to the reference resonator, each switchable capacitive module having a fixed capacitance and a variable capacitance, each switchable capacitive module responsive to a corresponding coefficient of a first plurality of calibration coefficients to switch between the fixed capacitance and the variable capacitance and to switch each variable capacitance to a control voltage. 
 
 
     
     
       28. The apparatus of  claim 27 , wherein the frequency controller further comprises:
 a second array having a plurality of switchable resistive modules coupled to the coefficient register and further having a capacitive module, the capacitive module and the plurality of switchable resistive modules further coupled to a node to provide the control voltage, each switchable resistive module responsive to a corresponding coefficient of a second plurality of coefficients stored in the coefficient register to switch the switchable resistive module to the control voltage node; and 
 a temperature-dependent current source coupled through a current mirror to the second array. 
 
     
     
       29. The apparatus of  claim 27 , further comprising:
 a negative transconductance amplifier coupled to the reference resonator; and 
 wherein the frequency controller is further adapted to modify a current through the negative transconductance amplifier in response to temperature. 
 
     
     
       30. The apparatus of  claim 29 , wherein the frequency controller further comprises a current source responsive to temperature. 
     
     
       31. An apparatus, comprising:
 a reference resonator adapted to provide a first reference signal having a resonant frequency; and 
 a frequency controller coupled to the reference resonator, the frequency controller adapted, when calibrated, to select the resonant frequency having a first frequency of a plurality of frequencies; and 
 a negative transconductance amplifier coupled to the reference resonator; 
 wherein the frequency controller is further adapted to modify a current through the negative transconductance amplifier in response to temperature; 
 wherein the frequency controller further comprises a current source responsive to temperature; and 
 wherein the current source further comprises one or more CTAT, PTAT, or PTAT 2  configurations. 
 
     
     
       32. The apparatus of  claim 31 , further comprising:
 a frequency divider coupled to the reference resonator, the frequency divider adapted to divide the first frequency by a rational number into a plurality of second signals having a corresponding plurality of frequencies, the plurality of frequencies substantially equal to or lower than the first frequency. 
 
     
     
       33. The apparatus of  claim 32 , wherein the frequency divider further comprises a square-wave generator, the square-wave generator adapted to convert the first reference signal into a substantially square-wave signal having a substantially equal high and low duty cycle. 
     
     
       34. An apparatus, comprising:
 a reference oscillator adapted to provide a first reference signal having an oscillation frequency; 
 an amplifier coupled to the reference oscillator; 
 a process variation compensator coupled to the reference oscillator, the process variation compensator adapted to determine the oscillation frequency when calibrated for fabrication process variation; and 
 a temperature compensator coupled to the amplifier or the reference oscillator, the temperature compensator adapted to maintain substantially the determined oscillation frequency of the reference oscillator in response to a temperature variation; 
 wherein the temperature compensator further comprises:
 a coefficient register adapted to store a first plurality of coefficients and a second plurality of coefficients; 
 a first array having a plurality of binary-weighted switchable capacitance branches coupled to the coefficient register and to the reference oscillator, each switchable capacitance branch having a fixed capacitance and a variable capacitance and responsive to a corresponding coefficient of the first plurality of coefficients to switch between the fixed capacitance and the variable capacitance and to switch the variable capacitance to a control voltage node; 
 a second array coupled to the control voltage node, the second array having a plurality of switchable resistances coupled to the coefficient register and further having a fixed capacitance, each switchable resistive module responsive to a corresponding coefficient of the second plurality of coefficients to switch the switchable resistive module to the control voltage node; and 
 a temperature-dependent current source coupled through a current mirror to the second array. 
 
 
     
     
       35. An apparatus, comprising:
 a reference oscillator adapted to provide a first reference signal having an oscillation frequency; 
 an amplifier coupled to the reference oscillator; 
 a process variation compensator coupled to the reference oscillator, the process variation compensator adapted to determine the oscillation frequency when calibrated for fabrication process variation; and 
 a temperature compensator coupled to the amplifier or the reference oscillator, the temperature compensator adapted to maintain substantially the determined oscillation frequency of the reference oscillator in response to a temperature variation; 
 wherein the process variation compensator further comprises:
 a coefficient register embodied as one or more memory circuits and adapted to store a first plurality of calibration coefficients; and 
 
 wherein the process variation compensator further comprises:
 a first array having a plurality of switchable capacitive modules coupled to the coefficient register and to the reference oscillator, each switchable capacitive module having a fixed capacitance and a variable capacitance, each switchable capacitive module responsive to a corresponding coefficient of the first plurality of calibration coefficients to switch between the fixed capacitance and the variable capacitance and to switch each variable capacitance to a control voltage. 
 
 
     
     
       36. An apparatus, comprising:
 a reference oscillator adapted to provide a first reference signal having an oscillation frequency; 
 an amplifier coupled to the reference oscillator; 
 a process variation compensator coupled to the reference oscillator, the process variation compensator adapted to determine the oscillation frequency when calibrated for fabrication process variation; and 
 a temperature compensator coupled to the amplifier or the reference oscillator, the temperature compensator adapted to maintain substantially the determined oscillation frequency of the reference oscillator in response to a temperature variation; 
 wherein the process variation compensator further comprises:
 a coefficient register embodied as one or more memory circuits and adapted to store a first plurality of calibration coefficients; and 
 
 wherein the process variation compensator further comprises:
 a first array having a plurality of switchable resistive modules coupled to the coefficient register and further having a capacitive module, the capacitive module and the plurality of switchable resistive Modules further coupled to a node to provide the control voltage, each switchable resistive module responsive to a corresponding coefficient of a second plurality of coefficients stored in the coefficient register to switch the switchable resistive module to the control voltage node; and 
 a temperature-dependent current source coupled through a current mirror to the second array. 
 
 
     
     
       37. The apparatus of  claim 36 , wherein the process variation compensator further comprises:
 an array having a plurality of switchable capacitive modules coupled to the coefficient register and to the reference oscillator, each switchable capacitive module having a first fixed capacitance and a second fixed capacitance, each switchable capacitive module responsive to a corresponding coefficient of the first plurality of calibration coefficients to switch between the first fixed capacitance and the second fixed capacitance.